Electricity lead-in body for bulb and method for manufacturing the same

ABSTRACT

The object of the invention to devise an electrical insertion body for a tube lamp in which sealing bodies of an electrically conductive inorganic material component and a dielectric inorganic material component and upholding parts of the electrodes are attached securely to one another by sintering, and in which neither leaks nor falling out of the upholding parts of the electrodes occur. The object is achieved as claimed in the invention, in an electrical insertion body for a tube lamp in which an upholding part of the electrode is inserted into the center opening of a respective sealing body of a functional gradient material for a tube lamp, in that in the boundary areas between the sealing bodies and the upholding parts of the electrodes one diffusion area at a time is formed, in which the electrically conductive inorganic material component of the sealing body, the metallic component of the upholding part of the electrode and a diffusion accelerator are present diffused into one another, which at the sintering temperature accelerates diffusion of the electrically conductive inorganic material component of the sealing body and of the metallic component of the upholding part of the electrode and that in this way the upholding part of the electrode and the electrically conductive inorganic material component of the sealing body are joined to one another.

TECHNICAL FIELD

The invention relates to an electrical insertion body for a tube lampwhich seals a sealing tube of a tube lamp, such as a mercury lamp, ametal halide lamp, a halogen lamp or the like. The invention furthermorerelates to a production process for the electrical insertion body. Theexpression “electrical insertion body for a tube lamp” is defined as anarrangement in which a sealing body is combined with an upholding partof the electrode.

DESCRIPTION OF RELATED ART

In a tube lamp, for example a high pressure discharge lamp, in aspherical or oval fused silica glass arc tube there are a pair ofelectrodes opposite one another and the tube is filled with an emissionmetal such as mercury or the like, discharge gas and the like.Cylindrical sealing tubes are connected to the ends of the arc tube.Upholding parts of the electrodes with tips each provided with anelectrode, and outer lead pins are electrically connected by thesesealing tubes and are sealed in this state. Since however the upholdingparts of the electrodes of tungsten and the sealing tubes of fusedsilica glass have very different coefficients of thermal expansion, thesealing tubes cannot be directly welded to the upholding parts of theelectrodes and sealed.

The sealing tubes were therefore conventionally sealed by a foil sealingprocess, a step joining process or the like. In the step joining processseveral types of glass with different coefficients of thermal expansionare joined to one another. Recently it has become more and moreimportant to seal sealing tubes which are connected to the ends of thearc tubes using sealing bodies which consist of a functional gradientmaterial which consists of a dielectric inorganic material componentsuch as silicon dioxide or the like and of an electrically conductiveinorganic material component such as molybdenum or the like and which ismade essentially columnar.

In this sealing body one end is rich in the dielectric inorganicmaterial component such as silicon dioxide or the like and in thedirection to the other end the proportion of electrically conductiveinorganic material component such as molybdenum or the like increasescontinuously or in steps.

In a sealing body of a functional gradient material which is formed fromsilicon dioxide and molybdenum, therefore the vicinity of one end of thesealing body contains a large amount of silicon dioxide, is dielectricand has a coefficient of thermal expansion which is roughly equal tothat of the fused silica glass, while the vicinity of the other endcontains a large amount of molybdenum, is electrically conductive andhas the property that its coefficient of thermal expansion approachesthat of the molybdenum.

Since in this sealing body of a functional gradient material thegradient of the change of the ratio of the dielectric inorganic materialcomponent to the electrically conductive inorganic material componentcan be increased, the one face side has a large proportion of thedielectric inorganic material component while the other face side canhave a large proportion of the electrically conductive inorganicmaterial component, even if the sealing body is not long in its axialdirection.

The functional gradient material has no interface on which thecomposition of its material components changes significantly. Thefunctional gradient material is therefore resistant to thermal shock andhas high mechanical strength. Therefore the locations to be sealed atwhich the sealing tubes and the sealing bodies are welded to one anotherapproach the center area of the arc tube which reaches a hightemperature during operation. Therefore there is the advantage that thelength of the sealing tubes can be decreased, the short length of thesealing tubes in the axial direction also contributing to thisadvantage.

If the sealing body is formed from a functional gradient material of theelectrically conductive inorganic material component and the dielectricinorganic material component, the following is done.

First a binder is added to these powders. By pressing it in a castingmold a columnar compact is obtained which is temporarily sintered at atemperature of roughly 1300° C. In this way a temporarily sintered bodyis obtained.

Next, drilling is done to produce a center opening which is used toinsert the upholding part of the electrode into the center axis of thistemporarily sintered body.

Alternatively, pressing is done in a casting mold with a projectingcomponent for forming the center opening. Thus a compact with a centeropening produced beforehand is obtained. It is temporarily sintered. Theupholding part of the electrode is inserted into the center opening ofthe temporarily sintered body. Afterwards complete sintering is done ata temperature of roughly 1750° C.

Since these materials shrink during sintering of the functional gradientmaterial by 10 to 20%, it is necessary for the center opening of thetemporarily sintered body to be made larger than the outside diameter ofthe upholding part of the electrode. If here the size of the centeropening is not enough, during complete sintering in the functionalgradient material a stress forms around the upholding part of theelectrode, as does subsequent cracking. Therefore the center openingmust be made somewhat larger than a stipulated value and in this waycracking is prevented even if the functional gradient material shrinksdue to complete sintering.

In this case the disadvantage was the following:

Due to variations of the diameter of the center opening, variations ofcontraction during complete sintering and for similar reasons theupholding parts of the electrodes are not arranged stably enough on thesealing bodies to tightly adjoin one another. In the case of a throughopening in which this center opening penetrates one face side of thesealing body as far as its other face side, the hermetic adhesionproperty is inadequate. Therefore, after complete sintering on the sideof the sealing body from which the upholding part of the electrodeprojects glass or brazing filler metal is applied as a deposit and thusleaking is prevented, this side projecting from the tube lamp to theoutside. Furthermore, in this way the attachment of the upholding partsof the electrode in the sealing bodies was ensured. In this processhowever there was the disadvantage that the working steps increased andproduction required high expense.

Furthermore, in the case of a center opening which extends from one faceside of the sealing body by a stipulated distance and which is thereforenot made continuous, there was no problem of leakage, but there was thedisadvantage that as a result of inadequate attachment the upholdingparts of the electrodes fall out due to vibration or the like, orsimilar defects. In this case it was also necessary to take somemeasures to ensure attachment of the sealing bodies to the upholdingparts of the electrodes after complete sintering.

SUMMARY OF THE INVENTION

Therefore the object of the invention to devise an electrical insertionbody for a tube lamp in which an upholding part of the electrode issecurely attached by sintering into the center opening of a sealing bodyof an electrically conductive inorganic material component and adielectric inorganic material component and in which neither leaks norfalling out of the upholding parts of the electrodes occur. Furthermorethe object of the invention is to devise a production process for this.

The object is achieved in the invention in an electrical insertion bodyfor a tube lamp for hermetic sealing of the sealing tubes which areconnected to the arc tube of the tube lamp in

that there are sealing bodies for the tube lamp in which one upholdingpart of the electrode at a time is inserted into the center openingwhich is provided in the sintered functional gradient material whichconsists of an electrically conductive inorganic material component andof a dielectric inorganic material component and which is shaped in theform of a multilayer column such that the ratio of the two componentschanges gradually in the axial direction,

that in the boundary areas between the above described sealing bodiesand the upholding parts of the electrodes one diffusion area at a timeis formed, in which the electrically conductive inorganic materialcomponent of the sealing body, the metallic component of the upholdingpart of the electrode and a diffusion accelerator are present diffusedinto one another, which at the sintering temperature of the abovedescribed functional gradient material accelerates diffusion of theelectrically conductive inorganic material component of the sealing bodyand of the metallic component of the upholding part of the electrode and

that in this way the upholding part of the electrode and the inside ofthe center opening of the sealing body are joined to one another.

The term “diffusion accelerator” in the invention is defined as amaterial which, at the sintering temperature of the functional gradientmaterial which forms the sealing body, dissolves in the metalliccomponent of the upholding part of the electrode and also in theelectrically conductive inorganic material component of the sealing bodyand accelerates diffusion of the above described electrically conductiveinorganic material component and the electrically conductive inorganicmaterial component of the sealing body into one another.

One such electrical insertion body for a tube lamp is advantageouslyproduced by the process of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of a high pressure discharge lamp in whichsealing parts of the arc tube are sealed in sealing bodies of afunctional gradient material using electrical insertion bodies for atube lamp which are each penetrated and held by an upholding part of theelectrode;

FIG. 2 shows a schematic of another high pressure discharge lamp inwhich sealing parts of the arc tube are sealed in sealing bodies of afunctional gradient material by electrical insertion bodies for a tubelamp in which upholding parts of the electrodes are held withoutpenetration;

FIG. 3 shows a schematic of important parts of the electrical insertionbody and process of the present invention;

FIG. 4 shows a schematic of the result of EDX analysis of the joiningsite between a sealing body and an upholding part of the electrode inthe conventional case that a diffusion accelerator is not used.

FIG. 5 shows a schematic of the result of EDX analysis of the joiningsite between a sealing body and an upholding part of the electrode in anembodiment of the invention in which a diffusion accelerator is used;

FIG. 6 shows a schematic of the result of EDX analysis of the joiningsite between a sealing body and an upholding part of the electrode in anembodiment of the invention in which a diffusion accelerator is used;

FIG. 7 shows a table of one example of the mixing ratio (% by weight) ofthe respective powders to one another and the thickness (mm) of therespective layer in the case in which nickel is used as the diffusionaccelerator;

FIG. 8 shows a schematic of the mixing ratio (% by weight) of therespective powders to one another and the probability that a leak willform;

FIG. 9 shows a schematic of important parts of the electrical insertionbody and process of the present invention; and

FIG. 10 shows a table of one example of the mixing ratio (% by weight)of the respective powders to one another and the thickness (mm) of therespective layer in the case in which chromium is used as the diffusionaccelerator.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following the invention is described using several embodimentsshown in the drawings.

FIG. 1 shows an example of a high pressure discharge lamp in whichelectrical insertion bodies as claimed in the invention are used for atube lamp which is a short arc xenon lamp with a rated output of 3 kW.The electrical insertion bodies as claimed in the invention for a tubelamp can also be used for another discharge lamp like a mercury lamp, ametal halide lamp, or the like.

In the embodiment of the invention an example is described in whichelectrical insertion bodies for a tube lamp are used for a dischargelamp. But they can also be used for a filament lamp with a tungstenfilament, such as a halogen lamp or the like. In a discharge lamp theupholding parts of the electrodes are each attached in the centeropening of the sealing body by sintering. In the case of using theelectrical insertion body as claimed in the invention for a tube lampfor a halogen lamp with a tungsten filament an upholding part of theelectrode is not attached in the center opening of the sealing body bysintering, but inner lead pins with tips which are connected to the endsof the tungsten filament are each attached in the center opening of thesealing body by sintering.

In FIG. 1 an arc tube 11 of fused silica glass has a spherical or anoval center region in which there are an anode 20 and a cathode 30 oftungsten opposite one another at a distance of for example 5 mm andxenon gas with a stipulated pressure is added as the discharge gas.Sealing tubes 12, 12 are connected to the two ends of the arc tube 11.The end of the respective sealing tube 12 is sealed with an electricalinsertion body 70 for a tube lamp which consists of a sealing body 50 offunctional gradient material and an upholding part 40 of the electrode,the functional gradient material consisting of an electricallyconductive inorganic material component and a dielectric inorganicmaterial component.

The sealing body 50 is installed in the sealing tube 12 such that onedielectric face side 51 runs in the direction to the arc tube 11, and iswelded on this face side 51 to the sealing tube 12 of fused silicaglass. Reference number 40 labels the upholding part of the electrode.The upholding part 40 of the electrode of the anode 20 and the upholdingpart 40 of the electrode of the cathode 30 consist of tungsten. Thedielectric face side 51 of the sealing body 50 consists for example ofroughly 100% silicon dioxide. Reference number 52 labels an electricallyconductive face which has a composition of 25% SiO₂+75% Mo.

The functional gradient material of silicon dioxide and molybdenum iscompletely sintered at roughly 1750° C. By a coating of the upholdingpart 40 of the electrode with a diffusion accelerator or by the factthat the sealing bodies 50 formed from the functional gradient materialcontain a diffusion accelerator, the diffusion accelerator at thesintering temperature together with the electrically conductiveinorganic material which forms the sealing body 50 forms a solidsolution and is melted.

This molten solid solution diffuses into the metallic component of theupholding parts 40 of the electrodes. In this way in the interfaceregion between the upholding part 40 of the electrode and the inside ofthe center opening of the sealing body 50 an area is formed in which theelectrically conductive inorganic material component which forms thesealing body 50, the diffusion accelerator and the metallic component ofthe upholding part 40 of the electrode are present diffused into oneanother. The upholding part 40 of the electrode and the inside of thecenter opening of the sealing body 50 are thus securely joined to oneanother and attached.

This prevents a high pressure gas within the arc tube 11 from leakingbetween the upholding part 40 of the electrode and the sealing body 50or the upholding parts 40 of the electrodes from falling out. Thereliability of the connection sites is therefore increased. Therefore itis no longer necessary to apply glass or brazing filler metal as adeposit to the face side 52 of the sealing body 50 from which theupholding part 40 of the electrode projects, as was conventionally thecase. In this way the working process can be simplified.

Alternatively, as is shown in FIG. 2, the two face sides 51 and 52 ofthe sealing body 50 can each be provided with a center opening which isnot continuous and extends as far as the electrically conductive area.The upholding part 40 of the electrode of the anode 20, the upholdingpart 40 of the electrode of the cathode 30, an anode terminal 22 and acathode terminal 32 can be electrically connected to the respectivecenter opening. In this case as well by a coating of the upholding part40 of the electrode with a diffusion accelerator or by the fact that thesealing bodies 50 formed from the functional gradient material contain adiffusion accelerator, the diffusion accelerator together with theelectrically conductive inorganic material which forms the sealing body50 forms a solid solution and is melted.

In this way in the interface region between the upholding part 40 of theelectrode and the inside of the center opening of the sealing body 50 anarea is formed in which the electrically conductive inorganic materialcomponent which forms the sealing body 50, the diffusion accelerator andthe metallic component of the upholding part 40 of the electrode arepresent diffused into one another. The upholding part 40 of theelectrode and the inside of the center opening of the sealing body 50are thus securely joined to one another and attached.

In the following the preferred embodiment of the invention described inclaim 2 is described in which a process for producing the electricalinsertion body which is described in claim 1 for a tube lamp isdescribed.

The electrically conductive inorganic material component and thedielectric inorganic material component of the functional gradientmaterial consist for example of a molybdenum powder with an averagegrain size of 1.0 micron and a silicon dioxide powder with an averagegrain size of 5.6 microns. As the first process several powder mixturesare formed in which the mixing ratio of the molybdenum powder to thesilicon dioxide powder was changed.

Besides the above described silicon dioxide powder, a powder of thecorresponding ceramic can also be used as the dielectric inorganicmaterial component of the functional gradient material when the arc tubeconsists of ceramic. That is, it is enough if it consists of the samematerial as the arc tube. It goes without saying that for theelectrically conductive inorganic material component of the functionalgradient material, besides molybdenum powder, a suitable powder of aconductive metal such as nickel, tungsten or the like can be used.

As the second process these powder mixtures are mixed with an organicbinder, for example a stearic acid solution of roughly 23%, and aredried. A cylindrical casting mold which has a projecting component for acenter opening is filled with these mixtures. In the case of afunctional gradient material the casting mold is filled with the powdermixtures such that the mixing ratio of the molybdenum powder to thesilicon dioxide powder changes gradually. The cylindrical casting moldis pressed from the outside for example with a load of 1.5 t/cm². Thus acolumnar compact is obtained in which a center opening is formed.

As the third process the resulting compact is sintered in a hydrogenatmosphere at 1200° C. for 30 minutes. Thus the organic binder iseliminated and a temporarily sintered body is obtained.

As the fourth process, on the surface of the respective upholding partof the electrode for example a chromium layer is formed as the diffusionaccelerator. The chromium layer is formed by a galvanization process, aprocess of dipping into a powder, a sputtering process or the like. Thisthickness of the chromium layer can be for example roughly 30 microns.

Chromium is a metal which forms a 100% solid solution for example bothwith tungsten which is selected as the upholding part of the electrodeand also with molybdenum which is selected as the electricallyconductive inorganic material component of the functional gradientmaterial at a sintering temperature of 1750° C. and is therefore activeas a diffusion accelerator.

The diffusion accelerator is not limited to chromium. It is enough if itdiffuses at the sintering temperature both into the upholding parts ofthe electrodes and also into the electrically conductive inorganicmaterial component of the sealing body and in this way at the same timeaccelerates diffusion of the metallic component of the upholding part ofthe electrode and the electrically conductive inorganic materialcomponent of the sealing body into one another, if furthermore in thisway in the respective interface area between the upholding part of theelectrode and the sealing body an area is formed in which diffusion intoone another takes place and when the upholding parts of the electrodesand the sealing bodies are reliably joined to one another and areattached.

The element which was selected as the diffusion accelerator at thetemperature for complete sintering of 1750° C. is dissolved inmolybdenum as the electrically conductive inorganic material componentof the sealing body and in tungsten as the metallic component of theupholding part of the electrode at least to 5 at %. Since its meltingpoint is relatively lower than that of molybdenum which acts as anelectrically conductive inorganic material component, and than that oftungsten which acts as the main material component of the electricallyconductive inorganic material of the upholding parts of the electrodes,the element is a metal which diffuses far into it.

In the example of molybdenum as the electrically conductive inorganicmaterial component which forms the sealing bodies, Cr, Al, Co, Fe, Ni,Hf, Ir, Nb, Os, Pt, Pd, Ru, Rh, Si, Ti, V, Ta, Zr, Re or the like or analloy thereof can be used as the diffusion accelerator as the metallicelement.

As the fifth process the upholding part 40 of the electrode with a layerof diffusion accelerator formed on its surface is inserted into thecenter opening of the temporarily sintered body. As is shown in FIG. 3,a state is obtained in which between the inner peripheral surface of thecenter opening of the sealing body 50 and the outer peripheral surfaceof the upholding part of the electrode there is a diffusion accelerator60.

Then sintering continues at 1750° C. for 10 minutes in a nonoxidizingatmosphere or in a vacuum of roughly 10⁻² Pa.

Mainly chromium at a temperature of greater than or equal to 1677° C. is100% dissolved in molybdenum and also in tungsten when an assessment ismade from a phase diagram of the chromium-molybdenum base and thechromium-tungsten base. The phase of the solid solution is alsopreserved at a lower temperature if the cooling rate in practice ishigh. Therefore no cavity is formed. Since the sintering temperature of1750° C. has approached the melting point of chromium, the diffusioncoefficient of tungsten and of molybdenum in chromium is extremely good.

Since at the sintering temperature a constant time was maintained andcooling was done, the chromium of the diffusion accelerator 60 which isshown in FIG. 3 has diffused into the molybdenum of the sealing bodies50 and tungsten of the upholding parts 40 of the electrodes as shown inFIG. 5; this is also described below. The molybdenum of the sealing body50 has at the same time diffused into the chromium of the diffusionaccelerator 60 and also into the tungsten of the metallic component ofthe upholding parts 40 of the electrodes. The tungsten as the metalliccomponent of the upholding parts 40 of the electrodes has diffused alsointo the chromium of the diffusion accelerator 60 and into themolybdenum of the sealing body 50.

As a result thereof, a state is obtained in which the molybdenum as theelectrically conductive inorganic material component and the tungsten asthe metallic component of the upholding parts of the electrodes are welldiffused into one another. Thus a well joined sealing body can beobtained.

The chromium as the diffusion accelerator together with the molybdenumas the electrically conductive inorganic material component which formsthe sealing bodies 50 forms a solid solution and is melted. The meltedsolid solution diffuses by flowing into the tungsten which forms theupholding parts 40 of the electrodes. In this way an area is formed inwhich the molybdenum as the electrically conductive inorganic materialcomponent which forms the sealing bodies 50, the chromium as thediffusion accelerator and the tungsten of the upholding parts 40 of theelectrodes are present diffused into one another. Thus the upholdingparts 40 of the electrodes are joined to the sealing bodies 50.

In the following an experimental example is described for confirmationof the action of the invention.

15% by weight silicon dioxide and 85% by weight molybdenum werehomogeneously mixed with one another and formed into a column. Thissealing body was provided with a continuous center opening and waspenetrated with a tungsten upholding part of the electrode with adiameter of 3 mm which was subjected to chromium galvanization in awidth of 5 mm and a thickness of 30 microns. Thus a sample of anelectrical insertion body for a tube lamp was made available. Thissample was sintered for 10 minutes in a vacuum atmosphere at 1750° C.and cut in a cross section in the axial direction which comprises thetungsten upholding part of the electrode. This cut surface was subjectedto EDX analysis (energy scattering x-ray spectral method).

FIG. 5 shows the result of EDX analysis. As becomes apparent from FIG.5, the tungsten (W) of the upholding part of the electrode of tungstenand molybdenum (Mo) as the electrically conductive inorganic materialcomponent of the sealing body are diffused into one another in thediffusion region and joined. The tungsten upholding part of theelectrode and the inside of the center opening of the sealing body werethus securely joined to one another.

In the area which was subjected to chromium galvanization, tungsten andmolybdenum were diffused into one another by greater than or equal to 10microns. As becomes apparent from FIG. 6, chromium was also diffused inonto the side of the upholding part of the electrode by roughly 10microns and onto the side of the sealing body by roughly 100 microns.

Furthermore, observation was done by electron microscope photographs.Here it was confirmed that between the tungsten upholding part of theelectrode and the sealing body there was no longer any boundary and thetwo were securely attached to one another.

Furthermore, for comparison purposes under the same conditions as inchromium galvanization the upholding part of the electrode was joined tothe sealing body without chromium galvanization having been done. FIG. 4shows the result of EDX analysis here. As became apparent from FIG. 4,hardly any diffusion of the tungsten and the molybdenum into one anotherwas found when chromium galvanization was not done, i.e. when there wasno diffusion accelerator.

In the present invention, using a cylindrical casting mold with aprojecting component for a center opening a compact with a centeropening is obtained. In one embodiment of the present invention,described in claim 3 the outer peripheral surface of the respectiveupholding part 40 of the electrode is coated with a diffusionaccelerator. Here the upholding part 40 of the electrode is placed inthe middle of the cylindrical casting mold. The cylindrical casting moldis filled with powder mixtures which have been formed by mixing with anorganic binder and pressed from the outside. Thus a compact is obtainedwhich is formed integrally with the upholding part 40 of the electrode.

In the following, one embodiment of the invention is described.

Several first powder mixtures are produced in which an electricallyconductive inorganic material component, for example molybdenum powder,and a dielectric inorganic material component such as silicon dioxidepowder are mixed with different mixing ratios to one another. Powder asthe diffusion accelerator, for example nickel, is mixed with at leastone type of the first powder mixtures with a volumetric ratio of forexample 5%, yielding a second powder mixture.

Next, the first powder mixtures and the second powder mixtures are mixedindividually with an organic binder. A cylindrical casting mold whichhas a projecting component for a center opening is filled with the firstpowder mixtures such that the ratio of the molybdenum powder to thesilicon dioxide powder changes gradually. The casting mold is nextfilled with second powder mixtures and then filled with the first powdermixtures such that likewise the ratio of the molybdenum powder to thesilicon dioxide powder changes gradually. Thus a powder layer structureis obtained. The cylindrical casting mold is pressed from the outside.This yields a compact consisting of many layers.

FIG. 7 shows one example of the mixing ratio (% by weight) of the powderand the thickness of the respective layer.

The above described compact is temporally sintered, yielding atemporarily sintered body. Next (fifth process) the upholding part 40 ofthe electrode is inserted into the center opening of the temporallysintered body obtained in the fourth process and completely sintered.

When using a functional gradient material with the mixing ratios shownin FIG. 7 the sealing body 50 consists of 12 layers as is shown in FIG.9. The first layer contains only silicon dioxide, while the second toeighth layers and the twelfth layer consist of mixtures of silicondioxide and molybdenum which were formed from the first powder mixtures.

The ninth to eleventh layers on the other hand are mixtures of silicondioxide, molybdenum and nickel which were formed from the second powdermixtures. The layers have different thicknesses as is shown in FIG. 7.However they are feasibly shown in FIG. 9 with the same thickness. Thistemporarily sintered body is sintered for 10 minutes in a nonoxidizingatmosphere or in a vacuum of roughly 10⁻² Pa at 1750° C.

By this complete sintering the nickel contained in the ninth to theeleventh layers together with the molybdenum which forms the sealingbody 50 forms a solid solution and is diffused in onto the side of theupholding part 4 of the electrode. In this way an area is formed inwhich tungsten, molybdenum and nickel are diffused into one another andjoined.

The same result as in FIG. 5 is also obtained in EDX analysis. Thismeans that in the diffusion region the tungsten of the tungstenupholding part of the electrode and the molybdenum are diffused into oneanother and joined. The upholding part 40 of the electrode and theinside of the center opening of the sealing body 50 are attachedsecurely to one another. This is caused by the diffusion accelerationaction of nickel.

Furthermore, observation was done by electron microscope photographs. Inthis case it was also confirmed that between the upholding part 40 ofthe electrode and the sealing body there was no longer any boundary andthe two were securely attached to one another.

Therefore this prevents leakage of high pressure gas from the boundarybetween the upholding part 40 of the electrode and the sealing body 50during operation.

The mixing ratio of nickel to molybdenum in FIG. 7 is 5% by weight.However the mixing ratio of the nickel to the molybdenum was changed andthese mixing ratios and the degree of formation of leaks were studied.FIG. 8 shows the result.

As becomes apparent therefrom, at a mixing ratio of nickel of 5% byweight and 10% by weight no leak occurs while at a mixing ratio ofnickel of 3% by weight and 20% by weight the probability of a leakincreases.

The reason for this is that at a mixing ratio of nickel of 3% by weightthe amount of nickel is too small and an area for sufficient diffusioninto one another is not formed. At a mixing ratio of nickel of 20% byweight the solution boundary of nickel and molybdenum into one anotheris great at 1750° C. Since however in the cooling process excessmolybdenum or excess nickel precipitates or a third phase forms, in thealloy there remains a cavity from which presumably a leak occurs.

In the present invention, a cylindrical casting mold with a projectingcomponent for a center opening is used and a compact with a centeropening is obtained. But it is also possible to proceed as follows:

The upholding part 40 of the electrode is placed in the middle of thecylindrical casting mold. The cylindrical casting mold is graduallyfilled with first and second powder mixtures which have been mixed withan organic binder. The cylindrical casting mold is pressed from theoutside. Thus a compact is obtained which is formed integrally with theupholding part 40 of the electrode.

The present invention was described above using one embodiment in whichnickel is used as the diffusion accelerator. A case of using chromium asthe diffusion accelerator is described below.

Several first powder mixtures are produced in which an electricallyconductive inorganic material component, for example molybdenum powder,and a dielectric inorganic material component such as silicon dioxidepowder, are mixed with different mixing ratios to one another. Chromiumpowder as the diffusion accelerator is mixed with at least one type ofthe first powder mixtures with a volumetric ratio of for example 5%,yielding second powder mixtures.

Next, the first powder mixtures and the second powder mixtures are mixedindividually with an organic binder. A cylindrical casting mold isfilled with the first powder mixtures such that the ratio of themolybdenum powder to the silicon dioxide powder changes gradually. Thecasting mold is next filled with the second powder mixtures and thenfilled with the first powder mixtures such that likewise the ratio ofthe molybdenum powder to the silicon dioxide powder changes gradually.Thus a powder layer structure is obtained. The cylindrical casting moldis pressed from the outside. This yields a compact consisting of manylayers.

FIG. 10 shows one example of the mixing ratio (% by weight) of thepowder and the thickness of the respective layer.

The above described compact is temporally sintered, yielding atemporarily sintered body. The upholding part 40 of the electrode isinserted into the center opening of the temporally sintered body.

When using a functional gradient material with the mixing ratios shownin FIG. 10 the sealing body 50 consists of 12 layers. The first layercontains only silicon dioxide, while the second to eighth layers and thetwelfth layer consist of mixtures of silicon dioxide and molybdenumwhich were formed from the first powder mixtures.

The ninth to eleventh layers on the other hand are mixtures of silicondioxide, molybdenum and chromium which were formed from the secondpowder mixtures. This temporarily sintered body is completely sinteredfor 10 minutes in a nonoxidizing atmosphere or in a vacuum of roughly10⁻² Pa at 1750° C.

By this complete sintering the chromium contained in the ninth to theeleventh layers together with the molybdenum which forms the sealingbody 50 forms a solid solution and is diffused in onto the side of theupholding part 4 of the electrode. In this way an area is formed inwhich tungsten, molybdenum and chromium are diffused into one anotherand joined.

The same result as in FIG. 5 is obtained also in EDX analysis in thiscase. This means that the tungsten of the tungsten upholding part of theelectrode and the molybdenum are diffused into one another in thediffusion area and joined. The upholding part 40 of the electrode andthe inside of the center opening of the sealing body 50 are attachedsecurely to one another. This is caused by the diffusion accelerationaction of chromium.

Furthermore, observation was done by electron microscope photographs. Inthis case it was also confirmed that between the upholding part 40 ofthe electrode and the sealing body 50 there was no longer any boundaryand the two were securely attached to one another.

Therefore this prevents leakage of high pressure gas from the boundarybetween the upholding part 40 of the electrode and the sealing body 50during operation.

COMMERCIAL APPLICATION

As was described above, in the interface area between the innerperipheral surface of the center opening of the sealing body offunctional gradient material; which consists of a electricallyconductive inorganic material component and a dielectric inorganicmaterial component, and the outer peripheral surface of the upholdingpart of the electrode, an area is formed in which the electricallyconductive inorganic material component, the diffusion accelerator andthe dielectric inorganic material component are diffused into oneanother. The upholding part of the electrode and the electricallyconductive inorganic material component of the sealing body are thusjoined to one another.

In this way the inside of the center opening of the sealing body and theupholding part of the electrode are attached securely to one another.This prevents leakage or the upholding parts of the electrodes fromfalling out. The reliability of the joining site of the upholding partof the electrode is therefore greatly increased.

Thus an electrical insertion body for a tube lamp is obtained which issuitable for sealing the sealing tubes of a tube lamp, such as a mercurylamp, a metal halide lamp, a halogen lamp or the like.

What we claim is:
 1. An electrical insertion body for a tube lamp forhermetic sealing of sealing tubes connected to an arc tube of the tubelamp, in which one upholding part of an electrode is inserted into acenter opening of a respective sealing body formed of a functionalgradient material which includes an electrically conductive inorganicmaterial component and a dielectric inorganic material component andwhich is shaped in the form of a multilayer column such that the ratioof the electrically conductive inorganic material component and thedielectric inorganic material component changes gradually in the axialdirection, comprising: a diffusion area formed in the boundary areasbetween the sealing body and the upholding part of the electrode, saiddiffusion area including a diffused combination of the electricallyconductive inorganic material component which forms the sealing body, ametallic component of the upholding part of the electrode and adiffusion accelerator, the diffusion area adapted to acceleratediffusion of the electrically conductive inorganic material componentwhich forms the sealing body and of the metallic component of theupholding part of the electrode at a sintering temperature of thefunctional gradient material to cause joining of the upholding part ofthe electrode and an inside portion of the center opening of the sealingbody.
 2. A process for producing an electrical insertion body for a tubelamp, comprising the steps of: mixing an electrically conductiveinorganic material component with a dielectric inorganic materialcomponent to produce powder mixtures; mixing said powder mixtures withan organic binder; filling a cylindrical casting mold with the mixtureof said powder mixtures and said organic binder, said casting moldincluding a projecting component for forming a center opening; pressingthe cylindrical casting mold from the outside to form a compact;temporarily sintering said compact to form a temporarily sintered body;coating an outer peripheral surface of an upholding part of an electrodewith a diffusion accelerator; inserting the upholding part of theelectrode into the center opening of the temporarily sintered body; andcompletely sintering the temporarily sintered body to cause joining ofthe upholding part of the electrode and an inside portion of the centeropening of the completely sintered body.
 3. A process for producing anelectrical insertion body for a tube lamp, comprising the steps of:mixing an electrically conductive inorganic material component with adielectric inorganic material component to produce powder mixtures;coating an outer peripheral surface of an upholding part of an electrodewith a diffusion accelerator; placing the upholding part of theelectrode in a center of a cylindrical casting mold; mixing said powdermixtures with an organic binder; filling a cylindrical casing mold withthe mixture of said powder mixtures and said organic binder; pressingthe cylindrical casting mold from the outside to form a compact;temporarily sintering said compact to form a temporarily sintered body;and completely sintering the temporarily sintered body to cause joiningof the upholding part of the electrode and an inside portion of a centeropening of the completely sintered body.